| Sixth General Session |
Nano Bio Applications
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Plasmonics: Optics at the Nanoscale
Professor Naomi Halas
Rice University, Houston, TX , USA
In recent years we have shown that certain topologies of metallic nanoparticles possess optical resonances that can be tuned by controlling the size and shape of the nanostructure. The vivid optical properties of metallic nanostructures are due to their plasmon, or collective electronic, resonances. The interesting observation that some nanoscale geometries support plasmons that are highly dependent on aspect ratio, such as concentric sphere nanoshells, provides a starting point for the Plasmon Hybridization model recently developed (Prodan et al., Science 302, 419 (2003)). This simple and intuitive picture shows that we can interpret their plasmon response of metallic nanostructures as being due to the mixing and “hybridization” of plasmons of simpler geometries, in direct analogy with the hybridization of electron wave functions in molecular orbital theory. Plasmon hybridization provides a “design rule” that guides the development of more complex nanostructures with an optical response we can both predict and experimentally realize. In general, metallic nanostructures present interesting, well-defined electromagnetic nanoenvironments for studying the effect of the local fields of these structures on nearby molecules, nanostructures, materials or substrates. One recent example that has emerged from our work is a utilization of the nanoshell geometry as a nanoengineered substrate on which the Surface Enhanced Raman Scattering (SERS) response can be precisely controlled and optimized, an extremely useful feature for chemical and biosensing applications.
Just beyond the wavelengths of visible light, the near infrared region of the optical spectrum provides a window of high optical transmissivity into the human body. Since the hybrid plasmon of nanoshells can be easily tuned into this spectral region, developing optical addressable diagnostic methods, devices, even therapies that are essentially noninvasive based on the plasmonic response of metallic nanostructures becomes possible. With bioengineers, we have developed a suite of applications for nanoshells in the human body, such as a nanoshell-based photothermal cancer therapy.
Molecular Analysis and Design of Silica Nanofabrication in Diatoms
Nils Kröger1,2 and Nicole Poulsen1
Georgia Institute of Technology, Atlanta, GA 30332-0400, USA
The formation of inorganic materials under the control of an organism (biomineralization) is a widespread biological phenomenon ranging from bone and teeth formation in vertebrates to biogenesis of magnetic nanoparticles in bacteria. The structures of biominerals are species specific characteristics and markedly different from the structures of the corresponding abiotically formed minerals, clearly demonstrating a genetic program controlling the mineral biogenesis process. Among the most remarkable biomineral forming organisms are diatoms, which are unicellular, eukaryotic algae producing intricately structured cell walls made of amorphous, hydrated SiO2 (silica) (see Figure).
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Figure. SEM images of diatom biosilica. Cell wall of Thalassiosira pseudonana (left, scale bar: 1 µm) and detail of this cell wall (second from left, scale bar: 0.2 µm). Cell wall of Stephanopyxis turris (second from right, scale bar: 10 µm) and details of this cell wall (right, scale bar: 1 µm). |
The ability of diatoms to generate mineralized structures with complex 3D shapes and periodic nanopatterns under ambient conditions by far exceeds the capabilities of present day materials engineering. Therefore, identifying the diatom silica forming machinery and establishing tools for its manipulation is expected to lead to novel routes to the production of nanostructured materials for a wide variety of applications. However, genetic manipulation of diatoms is still in its infancy, thus impeding the development of biotechnological methods for producing tailored nanomaterials.
Previously, a unique family of phosphoproteins, termed silaffins, have been isolated from the diatoms Cylindrotheca fusiformis and Thalassiosira pseudonana. Silaffins are tightly incorporated into the silica and have been implicated in the silica morphogenesis process. Characterization of the chemical structure of silaffins and their ability to influence silica morphogenesis in vitro supports this assumption, yet experimental tools have been lacking that allow in vivo analysis of the role of silaffins. We have established a genetic transformation system for the diatom T. pseudonana that allows overexpression of endogenous and foreign proteins. Using GFP as a marker protein, a method has been established that enables specific targeting and stable integration of foreign proteins into the diatom silica. This method can now be exploited for the in vivo analysis of silaffin function, and for designing nanopatterned silica matrices for specific applications.
Potential Application of Nano Scale Technology in Cell-Tissue Engineering Therapy
Prof. Dr. Mona K. Marei
Tissue engineering laboratories
Faculty of dentistry, Alexandria University
Tissue engineering is an area of inter disciplinary research performed world wide for obtaining living tissue replacement and therapy reducing the reliance on donor tissue and organs.
This therapeutic evolution of neo-tissue is governed by scaffold-cellular interaction which ideally should mimic the structure and biological function of native extra cellular matrix (ECM), both in terms of chemical and physical support for the cells.
The organization of biomaterials of native ECM at nano-scale and the occurrence of nanobiological pores appear to be key factors for the functioning of ECM.
In addition, cellular function is integrally related to morphology, so the ability to control cell shape in tissue engineering is essential to ensure proper cellular function in final product.
Precisely constructed nano scaffolding and micro scaffolding are needed to guide tissue repair and replacement in vessels and organs. Nano-fiber meshes enable vascular grafts with superior mechanical properties. Growth Factors and angiogenic factors can be encapsulated in biodegradable nano particles that are embedded in tissue scaffolds and substrates to enhance tissue regeneration.
The promise of tissue engineering lies in the challenge of imitating nature and in the new opportunity to meet the public needs in the future.
